My 5 year old son has started nodding his head, sniffing and making a high pitched hum noise when he does it. it is a quick jerking. eyes blinking too?

See his doctor ASAP.: Please call his doctor and have him seen this week. His doctor may want to have him seen by a pediatric neurologist as well. From your description, he may have a complex tic disorder.

? Tic: A tic is a sudden, repetitive movement or sound that can be difficult to control. Tics that involve movements are called motor tics and those that are sounds are called vocal tics. I would see the doctor.